The government had already ordered an inquiry into the future operation of the panel of scientists advising the Home Office on drug policy before the controversial sacking of its chairman, Professor David Nutt, the Guardian has learned.

The review of the effectiveness of the Advisory Council on the Misuse of Drugs (ACMD) will intensify concerns that ministers are downgrading the importance of independent scientific advice in formulating policy.

The purpose of the review "is to satisfy ministers that the ACMD ... is discharging its function that the committee was set up to deliver and that it continues to represent value for money". It is being carried out by Sir David Omand, a former Home Office permanent secretary, and is due to be completed early next year.

The disclosure came as the home secretary, Alan Johnson, agreed to urgent talks with his beleaguered advisory panel of drug experts after they officially warned him that more members were prepared to quit over the sacking of Nutt.

Johnson is facing growing anger from across the scientific community over the affair. His decision was condemned today by senior scientists and former government advisers, including Lord John Krebs, former head of the Food Standards Agency, and Mike Walport, director of the Wellcome Trust and a member of the prime minister's Council for Science and Technology.

Two leading figures quit the drugs advisory body on Sunday over the sacking. An official letter from the ACMD to Johnson tonight made clear that a majority of the remaining 28 members want assurances on how the government will view their advice in future.

"For some members these matters are of such seriousness as to raise the question whether they can, in good conscience, continue on the council," says their letter to the home secretary.

"In this situation members wish for clarity and assurances about how the ministers view the council's advice and will view the council's advice in the future."

The home secretary said today that the row was not an attack on science or scientists but about the way Nutt had conducted himself as principal drugs adviser. It also became clear that the sacking last Friday did not come out of the blue but was part of a row simmering since the ACMD chairman found himself rebuked sharply by Jacqui Smith in February when he compared the risks of ecstasy to those of horse-riding.

But among continuing protests from leading scientists the dispute may make the hunt for a new chief scientific adviser to the Home Office more difficult. The holder of the post, Professor Paul Wiles, steps down next month.

The ACMD letter was sent as it emerged that a wide-ranging review into the future operation of the ACMD is under way. In the Commons, Johnson played down the significance of the review, arguing that it was part of a normal Whitehall "quinquennial process" and tried to defuse the more general row with the scientists.

"I asked Prof Nutt to resign as my principal drugs adviser not because of the work of the council but because of his failure to recognise that as chair of ACMD his role is to advise rather than criticise government policy on drugs." Johnson said that in February, while awaiting publication of the government's position on the classification of ecstasy, Nutt published an article and "addressed the media on the appropriateness, or otherwise, of the government's policy framework, expressing a view that horse-riding was more dangerous than ecstasy".

"On Thursday October 29 Prof Nutt chose, without prior notification to my department, to initiate a debate on drugs policy in the national media, returning to the February decisions, and accusing my predecessor or distorting and devaluing scientific research," he told MPs.

"As a result, I have lost confidence in Prof Nutt's ability to be my principal adviser on drugs."

Nutt revealed today that the chairmen of two other Home Office scientific advisory committees had written to him saying they were "horrified" at his treatment. He also intensified his attack on the government's approach to science and said politicians didn't understand what facts meant: "Politicians believe that if they think something, it is true," he said.